1. Field of the Invention
This invention relates to a process for producing aluminum from clay or other aluminum containing raw material.
2. Description of the Prior Art
There are a number of processes for producing aluminum including the Toth process and the Bayer-Hall process. The Toth process has advantages over the currently used Bayer-Hall process, including the ability to use low-grade bauxites, clays, or other aluminum containing ores. Such ores are much more plentiful and cheaper than the high-grade bauxite which is required for the Bayer-Hall process.
The Toth process (U.S. Pat. Nos. 3,615,359; 3,615,360; 3,713,809; and 3,713,811) consists of the following steps:
(a) Chlorination of a calcined clay mixed with coke in a mixture of chlorine and silicon tetrachloride, which is recirculated from step (b) and added to suppress the chlorination of silica in the clay, PA1 (b) Separation of volatile chlorides and carbon oxides produced in step (a) by a suitable series of fractional condensation and purification stages to yield a pure liquid aluminum trichloride and by product chloride of silicon, iron, titanium, etc., PA1 (c) Reduction of the aluminum trichloride by manganese metal to produce aluminum metal and a salt mixture of aluminum trichloride and manganese chloride, PA1 (d) Separation of the aluminum and salt mixture produced in step (c) and evaporation of the salt mixure to produce solid manganese chloride and aluminum chloride vapor which is condensed and returned to the aluminum generator, PA1 (e) Oxidation of the manganese chloride to produce manganese oxide and chlorine which is returned to step (a) and, PA1 (f) Reduction of manganese oxide to produce manganese metal in a conventional blast furnace.
The use of a blast furnace to produce manganese metal does not appear to be economically feasible. A minimum of 3 tons of manganese must be used for each ton of aluminum in the manganese reduction of aluminum trichloride, and regeneration of manganese in a blast furnace will require large quantities of coke. For example, 1.5 tons of coke is required per ton of manganese in the blast furnace of 75% ferromanganese. On this basis, 4.5 tons of coke would be required per ton of aluminum. Furthermore, the blast furnace product would also contain large quantities of manganese carbide (Mn.sub.3 C.sub.7) which would not be as effective in reducing aluminum trichloride as would pure manganese. In addition, aluminum carbide (Al.sub.4 C.sub.3) is more stable than manganese carbide (Mn.sub.3 C.sub.7) so that carbon may be transferred to the aluminum during the manganese reduction step.
The major advantage of the Toth process is the use of clay which constitutes a major breakthrough in the production of aluminum. However, it has been found that unless extreme precautions are taken, the resulting aluminum is contaminated with undesirably large quantities of manganese as well as carbon which is also used in the Toth process. Indeed, carbon consumption in the process is 1000% greater than is used in the Bayer-Hall process.